The invention relates generally to an intelligent switch which is suitable for controlling the use of a battery driven device such as a flashlight, toy, motor or the like and, more particularly, is concerned with an intelligent electrical device of the kind described in the applicant's international application No. PCT/ZA99/00107.
In the PCT application mechanical switches function as a man-machine-interface (“MMI”) between the device and an operator. The MMI functions are controlled by very low current signals using touch pads, carbon coated membrane type switches or similar mechanisms. A microchip is responsive to input signals from the MMI and can, according to application, be used in various ways. For example with a flashlight the MMI may control the on/off operation of the flashlight, cause the flashlight to be turned off after a predetermined time, provide an indication of battery strength, or enable the flashlight to be operated with a desired flashing sequence. Various other features can also be achieved through the judicious use of the microchip and reference is made to the specification of the PCT application for a further description of such features.
The applicant is aware of a number of systems which provide an indication of the charge left in a battery.
Osterhout et al (U.S. Pat. No. 4,876,632) describes a circuit which detects the closed circuit voltage of a battery pack used in a flashlight. Based on predetermined reference voltages the battery life is shown in one of three categories. The circuit is activated by an on/off switch of a flashlight and does not function when the flashlight is off. This is to ensure that there is no power consumption when the flashlight is off. If however the circuit should function when the light is off the open circuit voltage of the battery will be measured and this will give a misleading indication of the available battery life.
Mallory (U.S. Pat. No. 4,499,525) and Weber (U.S. Pat. No. 5,821,697) relate to the provision of constant illumination by flashlights. Much can be gained in terms of quality of light and operating life of light bulbs by maintaining constant power through a light bulb. It is to be noted that in most instances the voltage which is supplied by a battery varies quite extensively over its usable life. Mallory makes use of an RC filter to determine an effective current and time measurement. Based on component selection the duty cycle of a current delivered to a light bulb at a specific voltage can be determined.
Weber uses a different technique wherein power is dissipated in a variable resistor or transistor element. This approach is wasteful of power.